N-doped carbon nanotubes formed in a wide range of temperature and ramping rate for fast sodium storage

Herein, nickel@nitrogen-doped carbon nanotubes (Ni@NCNTs) are prepared by a simple and reliable method with Ni-based complex as single-source precursor. Significantly, the formation of CNTs is not susceptible to the calcination temperature and ramping rate and Ni@NCNTs can be attained from 430 to 900 °C in an inert atmosphere. Then they are the first time to be applied as the anode material for sodium–ion batteries. The presence of Ni nanoparticles (NPs) facilitates the solid electrolyte interface film over the anode surface and improves the capacity retention of the host material, especially at the high rates. Furthermore, Na+ diffusion is reinforced after the introduction of Ni NPs. Ni@NCNTs obtained at 500 °C (Ni@NCNTs-500) exhibit the best capacity retention and rate capability. Kinetics analyses demonstrate the faster electron transportation and ion diffusion than others prepared at other temperatures. The surficial capacitance storage favors the fast electrochemistry kinetics. It delivers a high specific capacity (192 mA h g−1 at 0.5 A g−1), excellent cycling stability (103 mA h g−1 after 10,000 cycles at 10 A g−1), and outstanding high-rate capability up to 20 A g−1 (118 mA h g −1). The related full cells confirm a high energy density of 140 Wh kg−1 at 38.16 W kg−1 and 44.27 W h kg−1 at 762 W kg−1.